Referring to FIGS. 1 and 2, a blowout preventer 10 has a body 12, rams 14 that carry ram blocks 16, and an internal cavity 18 that is closed by a pressure plate 20. The pressure plate 20 is removable to allow access to the interior cavity 18 to service the blowout preventer 10, replace the ram blocks 16, etc. The depicted blowout preventer 10 is a “double gate”, although other designs, such as a single, triple, etc. gate design could also be used.
Referring to FIG. 3, the pressure plate 20 carries block guides 22 and is installed against a sealing area 24 on body 12 that surrounds the interior cavity 18 shown in FIG. 1. Referring to FIG. 4 through 6, the typical method to seal the pressure plate 20 is to provide an “o”-ring face seal 26 about each of the openings of the cavity 18. The “o”-rings 26 are contained in specifically sized grooves 28 that are machined into the pressure plate 20. The groove 28 is sized such that the seal 26 protrudes out of the face of the groove 28, as shown in FIG. 4. When the pressure plate 20 is installed, the “o”-rings 26 are compressed against the face of the body 12 and squeezed into the groove 28, as shown in FIG. 5. Referring to FIG. 4 through 6, the “o”-ring takes the general shape of the groove 28, but does not fill the entire volume and leaves spaces 30, particularly in the corners of the rectangular groove 28, as can be seen in FIG. 5. This compression of the “o”-ring seal 26 into the groove 28 initiates the seal to contain well bore fluids. When the internal pressure increases, the well fluids act against the “o”-rings 26 to maintain the seal. The well fluid pressure acts directly on the “o”-ring 26 to further compress it into the remaining spaces of the rectangular groove, as shown in FIG. 6. This seal system allows pressurized well fluid to act directly against the “o”-ring 26 and fill the groove 28. This action causes “wetting” of the groove 28 and face of the body 12 up to the “point of seal” against the “o”-ring 26.